This invention relates to high voltage electric power transmission systems, and more specifically relates to a novel hybrid system which permits the transmission of exceptionally high voltages using transmission tower heights and rights of way which are designed for a much lower transmission voltage.
The increase of voltage in high voltage high power transmission systems has led to numerous problems. For example, when the voltage of the transmission system is increased to 765 kV, the towers for supporting the conductors of the system must be extremely high and the spacing between the adjacent conductors of the multiphase system must be very wide. This requires substantial increases in the right of way needed for the transmission line and considerably increases the costs of the support towers.
There is also increasing concern over possibly harmful effects of the increased electric field produced by overhead transmission lines. This includes the possibility that the very high electric field strength around extremely high voltage (EHV) lines can charge objects such as fences, metal roofs, automobiles and the like to dangerous potentials. Moreover, living animals can themselves become charged to high potentials when in proximity in EHV transmission lines, as evidenced by the discharge sparking which can occur when a person near such a transmission line touches another object.
There is also concern over adverse effects on the health of human beings when in the sustained presence of the very high electric and magnetic fields produced by EHV transmission lines. Other problems which have been considered in connection with EHV transmission lines are that the higher voltages can cause television interference, radio interference and substantial audible noise.